IQUIMEFA   05518
INSTITUTO QUIMICA Y METABOLISMO DEL FARMACO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Role of endogenous nitric oxide in classic preconditioning in rat hearts
Autor/es:
MARÍA GABRIELA MARINA PRENDES; MARCELA GONZÁLEZ; ENRIQUE ALBERTO SAVINO; ALICIA VARELA
Lugar:
Ouro Preto, MG, Brasil
Reunión:
Congreso; VI International Symposium on Vasoactive Peptides; 2006
Resumen:
Objective: Preconditioning the heart with brief intermittent periods of ischemia has been shown to reduce infarct size and postischemic contractile dysfunction after a subsequent sustained period of ischemia. Although many endogenously released agents including adenosine, catecholamines, bradykinin and opioid peptides have been implicated in triggering the cardioprotective response, the intracellular signaling pathway that underlies this powerful defensive adaptation is not completely characterized and an additive activation of these preconditioning triggers could be required to reach a certain threshold beyond which cardioprotection becomes manifest (Yellon D M and Downey JM, Physiol Rev 89: 1113-1151, 2003). Despite a body of evidence implicating a pivotal role of the mitochondrial ATP-sensitive potassium channel (K-ATP) in the signal transduction pathway activated in response to ischemic preconditioning (IPC), not all data are supportive of this role. In this regard, 5-hydroxydecanoate, a selective K-ATP blocker abolished the beneficial effect of IPC on functional recovery but did not prevent the limitation of infarct size in Langendorff perfused rat hearts subjected to no flow global ischemia and reperfusion (Marina Prendes MG et al, Medicina Vol 65 SUPL II, pag. 171, 2005), suggesting that other subcellular mechanisms are involved. Interestingly, although nitric oxide (NO) has been shown to serve as a key mediator of the “second window” or late phase of IPC, its role in classic or acute preconditioning is limited and controversial. On these bases, it seemed interesting to examine a possible role of NO in the protective effects of acute IPC by means of the non specific inhibitor of nitric oxide synthase, N-nitro-L-arginine methyl ester (L-NAME). In order to meet this goal, the effects of L-NAME on postischemic recovery and cell viability following ischemia and reperfusion were tested in preconditioned hearts in relation to glycogen content and lactate production. Methods: Isovolumically beating isolated rat hearts perfused retrogradely with Krebs-Ringer bicarbonate buffer containing 10 mmol/L glucose were exposed to 25 min no flow global ischemia plus 30 min reperfusion (RP). IPC was achieved by a 3 min no flow global ischemia plus a 5 min reperfusion cycle before sustained ischemia. L-NAME (50 µM) perfusion begun 5 min before IPC or 13 min before sustained ischemia in the non preconditioned group until the end of ischemia. Contractility was evaluated by the left ventricular developed pressure-heart rate product (RPP) and contracture by left ventricular end diastolic pressure (LVEDP). Cell viability (CV) was determined by triphenyl tetrazolium chloride staining. Statistical analysis was performed by three ways ANOVA and Tukey comparison test (n=8/group). Results: The concentration of L-NAME used in this study did not alter functional baseline variables in control rat hearts. IPC reduced the amplitud of early reperfusion contracture (LVEDP at 5 min RP: 3.14±.80 vs 34.86±10.54 %, p<0.01), and improved reperfusion recovery of RPP (82.86±8.07 vs 59.28±9.16 at 30 min RP, p<0.05). Pretreatment with L_NAME did not affect recovery of non preconditined hearts (LVEDP: 31.50±8.06%, RPP: 51.8±13.60%) but abolished the beneficial effects of IPC (LVEDP 17.50±5.54 p<0.05, RPP: 51.80±13.60% p<0.05). Cardiac glycogen decreased during 25 min ischemia from 339.43±61.62 to 64.85±18.55 µg/100mg dw and lactate production was 153.70±14.23µmol/g dw in control hearts. IPC preserved glycogen content (304.12±47.96 to 184.49±31.26 p<0.05) and decreased lactate production (95.29±10.51 p<0.05). None of these metabolic parameters were affected by L-NAME (glycogen: 304.49±58.55 to 109.45±41.37 in non preconditioned hearts and 304.20±48.68 to 145.08 in IPC hearts; lactate: 151.25±9.04 in non preconditioned and 69.97±3.87 in IPC hearts). Cell viability was increased from 21±6% in control hearts to 60±8% in ICP hearts and was unaffected by L-NAME (25±7 % in non preconditioned and 55±6% in IPC hearts). Conclusion: These data suggest that endogenous NO do not exert a cardioprotective effect on no flow global ischemic-reperfused rat heart, but it is involved in the protection elicited by IPC against stunning in the surviving myocardium.